1. Field of Invention
The present invention relates generally to the field of fluid sample handling and/or interfacial rheology measurement at temperature and pressure conditions existing at the source of the sample, or at least temperatures different than ambient, including, but not limited to, reservoir hydrocarbon and aqueous based fluids, drilling muds, frac fluids, and the like having multiple phases (solids and liquid).
2. Related Art
Reservoir fluids often contain suspended particles under pressure and temperature conditions similar to those experienced in petroleum reservoirs and petroleum production systems. The particles may be in the form of a second liquid phase (hydrocarbon or aqueous based droplets) or in the form of a solid (organic or inorganic). The presence of these particles is related to the phase behavior of the petroleum fluid and thus, the nature and/or composition of these particles may change with changes in pressure, temperature, or overall composition. In order to improve understanding of the particle phase behavior, it is desirable to obtain samples of the suspended particles at defined pressure and temperature conditions for subsequent analytical characterization.
The phase behavior and physical properties of a reservoir fluid can be reasonably estimated through equation of state model(s) that have been tuned using experimental data. In such models, the fluid composition is normally described by lumped values (or pseudo components) that represent the average behavior of various portions within the fluid, such as C30+ compositions or SARA fractions. In the case of C30+ compositions, acceptable average critical values are assigned to each pseudo component so that the collection of pseudo components can be used in simulation packages to calculate the phase behavior and properties of each phase. While providing simplification of the simulation and analysis, such averaging can result in the loss of small, yet important variations in chemical composition that can affect large-scale behaviors. Examples of such behavior that have been observed in recent literature and internal studies are described below.
Multiple Liquid Phases: The formation of a second liquid phase in the form of micron sized droplets has been recently observed for some Gulf of Mexico fluids under near critical conditions. Recent studies have also demonstrated the ability of heavy and bituminous oils to form multiple liquid phases under various conditions, particularly when solvent has been added to the system (J. M. Shaw and E. Behar, Fluid Phase Equilibria, 209 (2003) 185-206). An asphaltene-rich liquid phase has also been observed in reservoirs where there is contact between the reservoir fluid and free gas and/or water phase. While it is known that this asphaltene-rich liquid forms a “tar-mat” in the reservoir, the compositional details or the mechanism of tar-mat formation are not known.
In all three of these examples, there is little known about the composition of the different liquid phases or their physical properties. Without this knowledge, it is impossible to develop the necessary equation of state (EOS) models or to be able to accurately simulate flow through porous media. While it is possible to experimentally determine the conditions at which different phases exist (see, for example, Shaw, J. M. et al., Fluid Phase Equilibria, 209 (2003) 185-206), it is not currently possible to isolate and sample the individual liquid phases under high pressure, high temperature conditions. Isolation of these phases is required to perform detailed composition and physical property analysis of each phase under various temperature and pressure conditions.
Asphaltene Precipitation and Deposition: Asphaltenes are heavy, highly aromatic molecules that often precipitate from oils due to reductions in pressure and/or temperature or blending with incompatible fluids (see A. Hammami and J. Ratulowski in: Asphaltenes, Heavy Oils and Petroleomics, Oliver C. Mullins, Eric Y. Sheu, Ahmed Hammami, Alan Marshall, Editors, Kluwer Academic Publications, PRECIPITATION AND DEPOSITION OF ASPHALTENES IN PRODUCTION SYSTEMS: A FLOW ASSURANCE OVERVIEW, Chapter 23, 2006). Asphaltenes also contain multiple polar compounds; including oxygen, nitrogen, and sulphur that make the asphaltene molecules surface active. This surface activity leads to asphaltene deposition on the walls of process equipment and transportation pipelines and allows asphaltene to participate in the stabilization of water-in-oil emulsions. The “strength” of the surface activity of individual asphaltene molecules is dependent on the variation in asphaltene composition. There is experimental evidence that a small, specific sub-fractions of the asphaltene is responsible for the deposits found on solid surfaces (see, for example, M. Zougari, S. Jacobs, A. Hammami, G. Broze, M. Flannery, J. Ratulowski and A. Stankiewicz, “Novel Organic Solid Deposition and Control Device for Live Oils: Design and Applications” Energy & Fuels, 20 (2006) 1656-1663).
Current experimental methods of studying asphaltenes in reservoir fluids involve the detection of solid precipitation in visual or non-visual pressure-volume-temperature (PVT) cells. A hydrocarbon-based fluid would be placed inside the PVT cell under pressure and temperature conditions similar to those experienced within a petroleum reservoir or in the petroleum production process. The pressure and/or temperature of the fluid would then be changed to induce the formation of a solid precipitate (e.g. asphaltene). Detection of solid formation in the hydrocarbon fluid may be done using near-infrared detectors, x-ray detection, or visual detection via a high pressure, high temperature microscopy method. These detection methods are limited to suspended particle detection only and cannot isolate or sample individual particles for subsequent analysis.
In the case of precipitated asphaltenes, high-temperature, high-pressure filtration may be used to collect the asphaltene aggregates and/or flocs. While commonly used, the high-pressure, high-temperature filtration process contains some potentially serious limitations to the analysis of asphaltene precipitate. The first and obvious limitation is that the floc size and amount of the recovered asphaltene depends on the pore size of the filter. Also, one must be very careful not to cause precipitated solids (wax and/or asphaltenes) to grate through the pores of the filter by creating too large of a pressure drop across the filter. Secondly, asphaltenes collected by filtration often contain trapped oil that contains dissolved organic solids (wax or asphaltene). There is a risk that these dissolved solids, particularly asphaltenes, can be precipitated during the removal of the trapped oil. The solids from the trapped oil would then be carried through with the filtered asphaltene precipitate, thus representing a “contaminant” that can affect subsequent analytical characterization. Finally, any measurements completed on the filtered solids (e.g., asphaltene) will only provide information about “average” asphaltene properties. The current protocols do not permit sampling and analysis of individual flocs and/or aggregates, an exercise that may reveal possible variations in chemical composition between the aggregates. With selective high-temperature, high-pressure micro-sampling, it may be possible to detect these compositional variations that contribute to both the surface activity and aggregation behavior of asphaltenes.
Few devices are disclosed in the patent literature for micro-sampling of process fluids. One such device is disclosed in U.S. published patent application Ser. No. 20040217059 A1 (Coville et al.), which discloses a method and apparatus for directly sampling a fluid for micro-filtration. In this device the fluid sample from a main container is filtered through a membrane before it is injected into a collecting chamber by a piercing instrument. The sample of interest in this micro-filtration device is the separated particulates, although the filtrate could also be sampled for analysis. The micro-filtration device is intended for mean filtration of a specimen to separate particles from about 0.01 micrometers to about 20 micrometers in size as measured in the longest dimension of the particle. A pressure source (air) is used to push the fluid through the membrane. Although this micro-filtration/sampling device could be used for any general micro-filtration, its intended use is for the filtration of blood samples. Again the device is not rated to the pressure and temperature range of interest in the micro-sampling of hydrocarbon reservoir fluids.
United States Published Patent application Ser. No. 20040232075 A1 (Wells), discloses a device and method to wash and concentrate (adjust composition of) solid particles from a suspension sample. A filter membrane is used to produce a permeate (fluid with no solids) flow low in solid particulates. A back-flushing mechanism was introduced to remove the solid particles from the membrane surface to recover filtration efficiency. The maximum allowable differential pressure across the membrane is 14.5 psi. As such the operating pressure was limited to atmospheric conditions. Maximum allowable fluid viscosity is 5 cP.
A micro-sampling device for collecting a pressurized liquid or gas sample for injection into a chromatography apparatus was disclosed in U.S. Pat. No. 4,688,436 (Richon et al). The device isolates a small volume of the reservoir fluid under the actual pressure and temperature before introducing it into a chromatograph carrier gas stream, thus carrying the total sample into the chromatograph. No measure of pressure and temperature ratings and sample volume is provided in the document.
Micro-sampling has been extensively used in the medical, biological, and botanical sciences to collect specimen (micro-samples from living tissues and cells). One such instrument is the pressure probe described by Tomos et al., “The pressure probe: A versatile tool in plant cell physiology”, Annual Review of Plant Physiology and Plant Molecular Biology, 50 (1999), 447-472, which has evolved from an instrument for measuring cell turgor and other water relation parameters into a device for sampling the content of individual higher plant cells in situ in the living plant. Obviously the so-called pressure probe is not suited for the pressure and temperature range of interest for hydrocarbon phase behavior. Another minimally invasive technique was described by del Fabbro, “An improved technique for studying pleural fluid pressure and composition in rabbits”, Experimental Physiology, 83 (1998), 435-448, where capillary tubes were used to monitor the pleural fluid pressure and composition in live rabbits. The method included connecting polyethylene tubes to pleural space that provided means of measuring the pressure and collecting sub-samples from the pleural space.
In addition to sample collection from living organisms, the selection and manipulation of suspended particles is common practice in biological and emulsion studies. A common technique utilizes glass micropipettes to capture and manipulate individual droplets or cells within an aqueous or hydrocarbon media at atmospheric pressure and near ambient temperature conditions (see for example Moran, “Micro-Mechanics of Emulsion Drops”, PhD Thesis, University of Alberta, Edmonton, 2001). A schematic illustration is presented in FIG. 1. The technique involves placing a liquid containing suspend particles into a small glass container 16 open on two sides. Container 16 is then placed beneath a light source 2 such that individual particles may be observed, with the assistance of a microscope 4. As indicated in the inset view 14, one or more micropipettes 18, 20 are then inserted through the open sides of glass container 16 such that the tips of the micropipettes may be observed through microscope 4. Three-dimensional manipulators 6, 7 are then used to move the tips of the micropipettes and thus capture and manipulate suspended particles 22. A power source 8 powers light source 2, and may power a VCR 10 (which may record the images) and a monitor 12.
Glass micro-pipettes has also been used to investigate the interfacial rheology of liquid droplets (see for example Moran et al., “Shape relaxation of an elongated viscous drop”, Journal of Colloid and Interface Science, 267 (2003), 483-493). In another application of the glass micro-pipettes (micro-cantilever technique), the strength and breakup of flocs (aggregates) have been studied (Yeung A. K. C and Pelton R., “Micromechanics: A New Approach to Studying the Strength and Breakup of Flocs”, Journal of Colloids and Interface Science, 184 (1996), 579-585).
A long, but heretofore unmet, need exists in the art for apparatus and methods for isolating and/or measuring interfacial rheological properties of a portion of a sample at temperatures and pressures representing those existing at the source of the sample, or at least different than ambient laboratory conditions.